Pigments that are used in inks or other nonpolar environments must be readily dispersible and must be hydrophobic. Among the most important pigments are those comprised of a transition metal or an oxide or complex thereof. Accordingly, it is important to be able to render hydrophobic the surface of such transition metal-containing pigment particles.
It is known, for example, to use surfactants to improve the dispersibility of such pigment particles, but the utility of such a process is usually limited. The use of surfactants usually does not, for example, eliminate agglomerates of the pigment particles that may already have been formed during the drying process used in the manufacture of such pigments.
Thus, a need exists for a fast and economical way to render hydrophobic the surface of transition metal-containing pigment particles, so that such particles can be easily dispersed in a wide variety of solvents or vehicle systems. Such a need is met by the method of the present invention.